Fiber coatings with low pullout force

ABSTRACT

Fiber coatings with low Young&#39;s modulus, low fiber pullout force for fibers in the as-drawn state, and small time-dependent increases in pullout force as the fiber ages. The fiber coatings are cured products of coating compositions that include an oligomer formed from an isocyanate, a hydroxy acrylate compound and a polyol. The oligomer includes a polyether urethane acrylate and a di-adduct compound. The reaction mixture used to form the oligomer includes a molar ratio of isocyanate:hydroxy acrylate:polyol of n:m:p, where when p is 2, n is in the range from 3.0 to 5.0 and m is in the range from 1.50n-3 to 2.50n-5. Control of the n:m:p ratio leads to compositions that, when cured, provide coatings and cured products having low Young&#39;s modulus, low pullout force on glass, and weak variations with time as the fiber ages.

This application claims the benefit of priority to U.S. ProvisionalApplication Ser. No. 62/666,376 filed on May 3, 2018, the content ofwhich is relied upon and incorporated herein by reference in itsentirety.

FIELD OF THE DISCLOSURE

This disclosure pertains to fiber coatings with good strippability forsplicing. More particularly, this disclosure pertains to primary fibercoatings with low pullout force and strong cohesion.

BACKGROUND OF THE DISCLOSURE

The transmissivity of light through an optical fiber is highly dependenton the properties of the coatings applied to the fiber. The coatingstypically include a primary coating and a secondary coating, where thesecondary coating surrounds the primary coating and the primary coatingcontacts the glass fiber (which includes a central glass core surroundedby a glass cladding). The secondary coating is a harder material (higherYoung's modulus) than the primary coating and is designed to protect theglass waveguide from damage caused by abrasion or external forces thatarise during processing, handling, and installation of the fiber. Theprimary coating is a softer material (low Young's modulus) and isdesigned to buffer or dissipates stresses that result from forcesapplied to the outer surface of the secondary coating. Dissipation ofstresses within the primary layer attenuates the stress and minimizesthe stress that reaches the glass waveguide. The primary coating isespecially important in dissipating stresses that arise when the fiberis bent. The bending stresses transmitted to the glass waveguide on thefiber needs to be minimized because bending stresses create localperturbations in the refractive index profile of the glass waveguide.The local refractive index perturbations lead to intensity losses forthe light transmitted through the waveguide. By dissipating stresses,the primary coating minimizes bend-induced intensity losses.

To minimize bending losses, it is desirable to develop primary coatingmaterials with increasingly lower Young's moduli. Coating materials witha Young's modulus below 1 MPa are preferred. As the Young's modulus ofthe primary coating is reduced, however, cohesion of the primary coatingdeteriorates and the primary coating is more susceptible to damage inthe fiber manufacturing process or during deployment in the field.Operations such as stripping, cabling, and connecting introduce thermaland mechanical stresses to the primary coating that can that lead to theformation of defects in the primary coating. The formation of defects inthe primary coating becomes more problematic as the cohesion of theprimary coating decreases.

In addition to good cohesion, fiber stripping and splice operationsrequire primary coatings with proper adhesion to the glass fiber. If theadhesion of the primary coating to the glass fiber is too strong,residue from the primary coating remains on the glass fiber and it isdifficult to achieve a clean strip. A clean strip is needed to insertthe glass fiber into a connector. The opening in fiber connectors isclosely matched to the diameter of the glass fiber and the presence ofcoating residue on the glass fiber prevents insertion of the fiber intoa connector. The adhesion requirements are particularly stringent forribbons, which are linear fiber assemblies that include multiple fibersin a common matrix. When connecting ribbons, all fibers are strippedsimultaneously and each fiber must be stripped cleanly withoutintroducing defects in the coating remaining on the unstrapped portionof the glass fiber.

There is a need for a primary coating material that can be cleanlystripped from glass fibers while also having sufficient cohesion toresist formation of defects when the stripping force is applied.

SUMMARY

The present disclosure provides primary coatings formed as curedproducts of curable compositions. The coatings feature low Young'smodulus, low pullout force and good cohesion. The variation in pulloutforce over time is low, indicating stable adhesion and consistentperformance of the coating over time. The coatings can be used asprimary coatings for optical fibers. The primary coatings can bestripped cleanly from glass fiber and are resistant to defect formationwhen subjected to stripping forces. The primary coatings can be appliedto individual fibers or to each of multiple fibers in a ribbon. Thecurable compositions can also be used to form cured films and othercured products used in applications outside the field of optical fibers.

The present description extends to:

A primary coating for optical fibers comprising:

-   -   a cured product of a curable composition, said cured product        comprising:        -   a Young's modulus less than 1.0 MPa; and            -   a pullout force less than 1.7 lb_(f)/cm when configured                as a primary coating with thickness 32.5 μm on a glass                fiber having a diameter of 125 μm in an as-drawn state,                said fiber pullout force increasing by less than a                factor of 2.0 upon aging said primary coating on said                glass fiber for at least 60 days.

The present description extends to:

An optical fiber comprising:

-   -   a glass core;    -   a glass cladding surrounding and in direct contact with said        glass core; and    -   a primary coating surrounding and in direct contact with said        glass cladding, said primary coating comprising:        -   a cured product of a curable composition, said cured product            comprising:            -   a Young's modulus less than 1.0 MPa; and            -   a pullout force less than 1.7 lb_(f)/cm when configured                as a primary coating with thickness 32.5 μm on a glass                fiber having a diameter of 125 μm in an as-drawn state,                said fiber pullout force increasing by less than a                factor of 2.0 upon aging said primary coating on said                glass fiber for at least 60 days.

The present disclosure further includes fiber coatings and curedproducts formed from the oligomers or coating compositions describedherein. The fiber coating features low Young's modulus, low pulloutforce and small increases in pullout force with aging.

The present disclosure further includes an optical fiber coated with acoating formed from a composition disclosed herein, wherein the opticalfiber includes a glass waveguide and the coating surrounds and is indirect contact with the glass waveguide.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings are illustrative of selected aspects of thepresent disclosure, and together with the description serve to explainprinciples and operation of methods, products, and compositions embracedby the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a coated optical fiber according oneembodiment.

FIG. 2 is a schematic view of a representative optical fiber ribbon. Therepresentative optical fiber ribbon includes twelve coated opticalfibers.

FIG. 3 shows force as a function of time in a pullout force test of afiber sample.

FIG. 4 shows variation in pullout force with time for a fiber sample.

FIG. 5 shows variation in pullout force with time for a fiber sample.

FIG. 6 shows variation in pullout force with time for a fiber sample.

FIG. 7 shows variation in pullout force with time for a fiber sample.

FIG. 8 shows variation in pullout force with time for a fiber sample.

DETAILED DESCRIPTION

The present disclosure is provided as an enabling teaching and can beunderstood more readily by reference to the following description,drawings, examples, and claims. To this end, those skilled in therelevant art will recognize and appreciate that many changes can be madeto the various aspects of the embodiments described herein, while stillobtaining the beneficial results. It will also be apparent that some ofthe desired benefits of the present embodiments can be obtained byselecting some of the features without utilizing other features.Accordingly, those who work in the art will recognize that manymodifications and adaptations are possible and can even be desirable incertain circumstances and are a part of the present disclosure.Therefore, it is to be understood that this disclosure is not limited tothe specific compositions, articles, devices, and methods disclosedunless otherwise specified. It is also to be understood that theterminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

“Include,” “includes,” or like terms means encompassing but not limitedto, that is, inclusive and not exclusive.

The term “about” references all terms in the range unless otherwisestated. For example, about 1, 2, or 3 is equivalent to about 1, about 2,or about 3, and further comprises from about 1-3, from about 1-2, andfrom about 2-3. Specific and preferred values disclosed forcompositions, components, ingredients, additives, and like aspects, andranges thereof, are for illustration only; they do not exclude otherdefined values or other values within defined ranges. The compositionsand methods of the disclosure include those having any value or anycombination of the values, specific values, more specific values, andpreferred values described herein.

The indefinite article “a” or “an” and its corresponding definitearticle “the” as used herein means at least one, or one or more, unlessspecified otherwise.

The coatings described herein are formed from curable coatingcompositions. Curable coating compositions include one or more curablecomponents. As used herein, the term “curable” is intended to mean thatthe component, when exposed to a suitable source of curing energy,includes one or more curable functional groups capable of formingcovalent bonds that participate in linking the component to itself or toother components of the coating composition. The product obtained bycuring a curable coating composition is referred to herein as the curedproduct of the composition. The cured product is preferably a polymer.The curing process is induced by energy. Forms of energy includeradiation or thermal energy. In a preferred embodiment, curing occurswith radiation. Curing induced by radiation is referred to herein asradiation curing or photocuring. A radiation-curable component is acomponent that can be induced to undergo a curing reaction when exposedto radiation of a suitable wavelength at a suitable intensity for asufficient period of time. Suitable wavelengths include wavelengths inthe infrared, visible, or ultraviolet portion of the electromagneticspectrum. The radiation curing reaction preferably occurs in thepresence of a photoinitiator. A radiation-curable component may also bethermally curable. Similarly, a thermally-curable component is acomponent that can be induced to undergo a curing reaction when exposedto thermal energy of sufficient intensity for a sufficient period oftime. A thermally curable component may also be radiation curable.

A curable component includes one or more curable functional groups. Acurable component with only one curable functional group is referred toherein as a monofunctional curable component. A curable component havingtwo or more curable functional groups is referred to herein as amultifunctional curable component. Multifunctional curable componentsinclude two or more functional groups capable of forming covalent bondsduring the curing process and can introduce crosslinks into thepolymeric network formed during the curing process. Multifunctionalcurable components may also be referred to herein as “crosslinkers” or“curable crosslinkers”. Curable components include curable monomers andcurable oligomers. Examples of functional groups that participate incovalent bond formation during the curing process are identifiedhereinafter.

The term “molecular weight” when applied to polyols means number averagemolecular weight.

The term “(meth)acrylate” means methacrylate, acrylate, or a combinationof methacrylate and acrylate.

Values of Young's modulus, tear strength, tensile toughness and pulloutforce refer to values as determined under the measurement conditions bythe procedures described herein.

Reference will now be made in detail to illustrative embodiments of thepresent description.

The present description relates to curable coating compositions,coatings formed from the curable coating compositions, and coatedarticles coated or encapsulated by the coating obtained by curing thecurable coating compositions. In a preferred embodiment, the curablecoating composition is a composition for forming coatings for opticalfibers, the coating is an optical fiber coating, and the coated articleis a coated optical fiber. The present description also relates tomethods of making curable coating compositions, methods of formingcoatings from the curable coating compositions, and methods of coatingfibers with the curable coating composition. Coatings formed from thecurable coating compositions can be stripped cleanly from glass fiberand have strong cohesion.

One embodiment relates to a coated optical fiber. An example of a coatedoptical fiber is shown in schematic cross-sectional view in FIG. 1.Coated optical fiber 10 includes a glass optical fiber 11 surrounded byprimary coating 16 and secondary coating 18. In a preferred embodiment,the primary coating 16 is the cured product of a curable coatingcomposition in accordance with the present description.

The glass fiber 11 is an uncoated optical fiber including a core 12 anda cladding 14, as is familiar to the skilled artisan. Core 12 has ahigher refractive index than cladding 14 and glass fiber 11 functions asa waveguide. In many applications, the core and cladding have adiscernible core-cladding boundary. Alternatively, the core and claddingcan lack a distinct boundary. One such fiber is a step-index fiber.Another such fiber is a graded-index fiber, which has a core whoserefractive index varies with distance from the fiber center. Agraded-index fiber is formed basically by diffusing the glass core andcladding layer into one another. The cladding can include one or morelayers. The one or more cladding layers can include an inner claddinglayer that surrounds the core and an outer cladding layer that surroundsthe inner cladding layer. The inner cladding layer and outer claddinglayer differ in refractive index. For example, the inner cladding layermay have a lower refractive index than the outer cladding layer. Adepressed index layer may also be positioned between the inner claddinglayer and outer cladding layer.

The optical fiber may also be single or multi-mode at the wavelength ofinterest, e.g., 1310 or 1550 nm. The optical fiber may be adapted foruse as a data transmission fiber (e.g. SMF-28®, LEAF®, and METROCOR®,each of which is available from Corning Incorporated of Corning, N.Y.)Alternatively, the optical fiber may perform an amplification,dispersion compensation, or polarization maintenance function. Theskilled artisan will appreciate that the coatings described herein aresuitable for use with virtually any optical fiber for which protectionfrom the environment is desired.

The primary coating 16 preferably has a higher refractive index than thecladding of the optical fiber in order to allow it to strip errantoptical signals away from the optical fiber core. The primary coatingshould maintain adequate adhesion to the glass fiber during thermal andhydrolytic aging, yet be strippable from the glass fiber for splicingpurposes. The primary coating typically has a thickness in the range of25-40 μm (e.g. about 32.5 μm). Primary coatings are typically formed byapplying a curable coating composition to the glass fiber as a viscousliquid and curing.

FIG. 2 illustrates an optical fiber ribbon 30. The ribbon 30 includes aplurality of optical fibers 20 and a matrix 32 encapsulating theplurality of optical fibers. Optical fibers 20 include a core glassregion, a cladding glass region, a primary coating, and a secondarycoating as described above. Optical fibers 20 may also include an inklayer. The secondary coating may include a pigment. The optical fibers20 are aligned relative to one another in a substantially planar andparallel relationship. The optical fibers in fiber optic ribbons areencapsulated by the ribbon matrix 32 in any known configuration (e.g.,edge-bonded ribbon, thin-encapsulated ribbon, thick-encapsulated ribbon,or multi-layer ribbon) by conventional methods of making fiber opticribbons. In FIG. 2, the fiber optic ribbon 30 contains twelve (12)optical fibers 20; however, it should be apparent to those skilled inthe art that any number of optical fibers 20 (e.g., two or more) may beemployed to form fiber optic ribbon 30 disposed for a particular use.The ribbon matrix 32 can be formed from the same composition used toprepare a secondary coating, or the ribbon matrix 32 can be formed froma different composition that is otherwise compatible for use.

The present disclosure provides a primary coating for optical fibersthat exhibits low Young's modulus, low pullout force, and strongcohesion. The present disclosure provides curable coating compositionsthat enable formation of a primary coating that features cleanstrippability and high resistance to defect formation during thestripping operation. Low pullout force facilitates clean stripping ofthe primary coating with minimal residue and strong cohesion inhibitsinitiation and propagation of defects in the primary coating when it issubjected to stripping forces.

The primary coating is a cured product of a radiation-curable coatingcomposition that includes an oligomer, a monomer, a photoinitiator and,optionally, an additive. The present disclosure describes oligomers forthe radiation-curable coating compositions, radiation-curable coatingcompositions containing at least one of the oligomers, cured products ofthe radiation-curable coating compositions that include at least one ofthe oligomers, optical fibers coated with a radiation-curable coatingcomposition containing at least one of the oligomers, and optical fiberscoated with the cured product of a radiation-curable coating compositioncontaining at least one of the oligomers.

The oligomer includes a polyether urethane diacrylate compound and adi-adduct compound. In one embodiment, the polyether urethane diacrylatecompound has a linear molecular structure. In one embodiment, theoligomer is formed from a reaction between a diisocyanate compound, apolyol compound, and a hydroxy acrylate compound, where the reactionproduces a polyether urethane diacrylate compound as a primary product(majority product) and a di-adduct compound as a byproduct (minorityproduct). The reaction forms a urethane linkage upon reaction of anisocyanate group of the diisocyanate compound and an alcohol group ofthe polyol. The hydroxy acrylate compound reacts to quench residualisocyanate groups that are present in the composition formed fromreaction of the diisocyanate compound and polyol compound. As usedherein, the term “quench” refers to conversion of isocyanate groupsthrough a chemical reaction with hydroxyl groups of the hydroxy acrylatecompound. Quenching of residual isocyanate groups with a hydroxyacrylate compound converts terminal isocyanate groups to terminalacrylate groups.

A preferred diisocyanate compound is represented by molecular formula(I):O═C═N—R₁—N═C═O  (I)which includes two terminal isocyanate groups separated by a linkagegroup R₁. In one embodiment, the linkage group R₁ includes an alkylenegroup. The alkylene group of linkage group R₁ is linear (e.g. methyleneor ethylene), branched (e.g. isopropylene), or cyclic (e.g.cyclohexylene, phenylene). The cyclic group is aromatic or non-aromatic.In some embodiments, the linkage group R₁ is 4,4′-methylenebis(cyclohexyl) group and the diisocyanate compound is 4,4′-methylenebis(cyclohexyl isocyanate). In some embodiments, the linkage group R₁lacks an aromatic group, or lacks a phenylene group, or lacks anoxyphenylene group.

The polyol is represented by molecular formula (II):H—O

R₂—O

_(x)H  (II)where R₂ includes an alkylene group, —O—R₂— is a repeating alkoxylenegroup, and x is an integer. Preferably, x is greater than 20, or greaterthan 40, or greater than 50, or greater than 75, or greater than 100, orgreater than 125, or greater than 150, or in the range from 20-500, orin the range from 20-300, or in the range from 30-250, or in the rangefrom 40-200, or in the range from 60-180, or in the range from 70-160,or in the range from 80-140. R₂ is preferably a linear or branchedalkylene group, such as methylene, ethylene, propylene (normal, iso or acombination thereof), or butylene (normal, iso, secondary, tertiary, ora combination thereof). The polyol may be a polyalkylene oxide, such aspolyethylene oxide, or a polyalkylene glycol, such as polypropyleneglycol. Polypropylene glycol is a preferred polyol. The molecular weightof the polyol is greater than 1000 g/mol, or greater than 2500 g/mol, orgreater than 5000 g/mol, or greater than 7500 g/mol, or greater than10000 g/mol, or in the range from 1000 g/mol-20000 g/mol, or in therange from 2000 g/mol-15000 g/mol, or in the range from 2500 g/mol-12500g/mol, or in the range from 2500 g/mol-10000 g/mol, or in the range from3000 g/mol-7500 g/mol, or in the range from 3000 g/mol-6000 g/mol, or inthe range from 3500 g/mol-5500 g/mol. In some embodiments, the polyol ispolydisperse and includes molecules spanning a range of molecularweights such that the totality of molecules combine to provide thenumber average molecular weight specified hereinabove.

The unsaturation of the polyol is less than 0.25 meq/g, or less than0.15 meq/g, or less than 0.10 meq/g, or less than 0.08 meq/g, or lessthan 0.06 meq/g, or less than 0.04 meq/g, or less than 0.02 meq/g, orless than 0.01 meq/g, or less than 0.005 meq/g, or in the range from0.001 meq/g-0.15 meq/g, or in the range from 0.005 meq/g-0.10 meq/g, orin the range from 0.01 meq/g-0.10 meq/g, or in the range from 0.01meq/g-0.05 meq/g, or in the range from 0.02 meq/g-0.10 meq/g, or in therange from 0.02 meq/g-0.05 meq/g. As used herein, unsaturation refers tothe value determined by the standard method reported in ASTM D4671-16.In the method, the polyol is reacted with mercuric acetate and methanolin a methanolic solution to produce acetoxymercuricmethoxy compounds andacetic acid. The reaction of the polyol with mercuric acetate isequimolar and the amount of acetic acid released is determined bytitration with alcoholic potassium hydroxide to provide the measure ofunsaturation used herein. To prevent interference of excess mercuricacetate on the titration of acetic acid, sodium bromide is added toconvert mercuric acetate to the bromide.

The reaction to form the oligomer further includes addition of a hydroxyacrylate compound to react with terminal isocyanate groups present inunreacted starting materials (e.g. the diisocyanate compound) orproducts formed in the reaction of the diisocyanate compound with thepolyol (e.g. urethane compounds with terminal isocyanate groups). Thehydroxy acrylate compound reacts with terminal isocyanate groups toprovide terminal acrylate groups for one or more constituents of theoligomer. In some embodiments, the hydroxy acrylate compound is presentin excess of the amount needed to fully convert terminal isocyanategroups to terminal acrylate groups. The oligomer includes a singlepolyether urethane acrylate compound or a combination of two or morepolyether urethane acrylate compounds.

The hydroxy acrylate compound is represented by molecular formula (III):

where R₃ includes an alkylene group. The alkylene group of R₃ is linear(e.g. methylene or ethylene), branched (e.g. isopropylene), or cyclic(e.g. phenylene). In some embodiments, the hydroxy acrylate compoundincludes substitution of the ethylenically unsaturated group of theacrylate group. Substituents of the ethylenically unsaturated groupinclude alkyl groups. An example of a hydroxy acrylate compound with asubstituted ethylenically unsaturated group is a hydroxy methacrylatecompound. The discussion that follows describes hydroxy acrylatecompounds. It should be understood, however, that the discussion appliesto substituted hydroxy acrylate compounds and in particular to hydroxymethacrylate compounds.

In different embodiments, the hydroxy acrylate compound is ahydroxyalkyl acrylate, such as 2-hydroxyethyl acrylate. The hydroxyacrylate compound may include water at residual or higher levels. Thepresence of water in the hydroxy acrylate compound may facilitatereaction of isocyanate groups to reduce the concentration of unreactedisocyanate groups in the final reaction composition. In variousembodiments, the water content of the hydroxy acrylate compound is atleast 300 ppm, or at least 600 ppm, or at least 1000 ppm, or at least1500 ppm, or at least 2000 ppm, or at least 2500 ppm.

In the foregoing exemplary molecular formulas (I), III), and (III), thegroups R₁, R₂, and R₃ are all the same, are all different, or includetwo groups that are the same and one group that is different.

The diisocyanate compound, hydroxy acrylate compound and polyol arecombined simultaneously and reacted, or are combined sequentially (inany order) and reacted. In one embodiment, the oligomer is formed byreacting a diisocyanate compound with a hydroxy acrylate compound andreacting the resulting product composition with a polyol. In anotherembodiment, the oligomer is formed by reacting a diisocyanate compoundwith a polyol compound and reacting the resulting product compositionwith a hydroxy acrylate compound.

The oligomer is formed from a reaction of a diisocyanate compound, ahydroxy acrylate compound, and a polyol, where the molar ratio of thediisocyanate compound to the hydroxy acrylate compound to the polyol inthe reaction process is n:m:p. n, m, and p are referred to herein asmole numbers or molar proportions of diisocyanate, hydroxy acrylate, andpolyol; respectively. The mole numbers n, m and p are positive integeror positive non-integer numbers. When p is 2.0, n is in the range from3.0-5.0, or in the range from 3.0-4.5, or in the range from 3.2-4.8, orin the range from 3.4-4.6, or in the range from 3.6-4.4, and m is in therange from 1.50n-3 to 2.50n-5, or in the range from 1.55n-3 to 2.45n-5,or in the range from 1.60n-3 to 2.40n-5, or in the range from 1.65n-3 to2.35n-5. For example, when p is 2.0 and n is 3.0, m is in the range from1.5 to 2.5, or in the range from 1.65 to 2.35, or in the range from 1.80to 2.20, or in the range from 1.95 to 2.05. For values of p other than2.0, the molar ratio n:m:p scales proportionally. For example, the molarratio n:m:p=4.0:3.0:2.0 is equivalent to the molar ration:m:p=2.0:1.5:1.0.

The mole number m may be selected to provide an amount of the hydroxyacrylate compound to stoichiometrically react with unreacted isocyanategroups present in the product composition formed from the reaction ofdiisocyanate compound and polyol used to form the oligomer. Theisocyanate groups may be present in unreacted diisocyanate compound(unreacted starting material) or in isocyanate-terminated urethanecompounds formed in reactions of the diisocyanate compound with thepolyol. Alternatively, the mole number m may be selected to provide anamount of the hydroxy acrylate compound in excess of the amount neededto stoichiometrically react with any unreacted isocyanate groups presentin the product composition formed from reaction of the diisocyanatecompound and the polyol. The hydroxy acrylate compound is added as asingle aliquot or multiple aliquots. In one embodiment, an initialaliquot of hydroxy acrylate is included in the reaction mixture used toform the oligomer and the product composition formed can be tested forthe presence of unreacted isocyanate groups (e.g. using FTIRspectroscopy to detect the presence of isocyanate groups). Additionalaliquots of hydroxy acrylate compound may be added to the productcomposition to stoichiometrically react with unreacted isocyanate groups(using, for example, FTIR spectroscopy to monitor a decrease in acharacteristic isocyanate frequency (e.g. at 2260 cm⁻¹-2270 cm⁻¹) asisocyanate groups are converted by the hydroxy acrylate compound). Inalternate embodiments, aliquots of hydroxy acrylate compound in excessof the amount needed to stoichiometrically react with unreactedisocyanate groups are added. As described more fully below, for a givenvalue of p, the ratio of the mole number m to the mole number ninfluences the relative proportions of polyether urethane diacrylatecompound and di-adduct compound in the oligomer and differences in therelative proportions of polyether urethane diacrylate compound anddi-adduct compound lead to differences in the tear strength and/orcritical stress of coatings formed from the oligomer.

In one embodiment, the oligomer is formed from a reaction mixture thatincludes 4,4′-methylene bis(cyclohexyl isocyanate), 2-hydroxyethylacrylate, and polypropylene glycol in the molar ratios n:m:p asspecified above, where the polypropylene glycol has a number averagemolecular weight in the range from 2500 g/mol-6500 g/mol, or in therange from 3000 g/mol-6000 g/mol, or in the range from 3500 g/mol-5500g/mol.

The oligomer includes two components. The first component is a polyetherurethane diacrylate compound having the molecular formula (IV):

and the second component is a di-adduct compound having the molecularformula (V):

where the groups R₁, R₂, R₃, and the integer x are as describedhereinabove, y is a positive integer, and it is understood that thegroup R₁ in molecular formulas (IV) and (V) is the same as group R₁ inmolecular formula (I), the group R₂ in molecular formula (IV) is thesame as group R₂ in molecular formula (II), and the group R₃ inmolecular formulas (IV) and (V) is the same as group R₃ in molecularformula (III). The di-adduct compound corresponds to the compound formedby reaction of both terminal isocyanate groups of the diisocyanatecompound of molecular formula (I) with the hydroxy acrylate compound ofmolecular formula (III) where the diisocyanate compound has undergone noreaction with the polyol of molecular formula (II).

The di-adduct compound is formed from a reaction of the diisocyanatecompound with the hydroxy acrylate compound during the reaction used toform the oligomer. Alternatively, the di-adduct compound is formedindependent of the reaction used to form the oligomer and is added tothe product of the reaction used to form the polyether urethanediacrylate compound or to a purified form of the polyether urethanediacrylate compound. The hydroxy group of the hydroxy acrylate compoundreacts with an isocyanate group of the diisocyanate compound to providea terminal acrylate group. The reaction occurs at each isocyanate groupof the diisocyanate compound to form the di-adduct compound. Thedi-adduct compound is present in the oligomer in an amount of at least1.0 wt %, or at least 1.5 wt %, or at least 2.0 wt %, or at least 2.25wt %, or at least 2.5 wt %, or at least 3.0 wt %, or at least 3.5 wt %,or at least 4.0 wt %, or at least 4.5 wt %, or at least 5.0 wt %, or atleast 7.0 wt % or at least 9.0 wt %, or in the range from 1.0 wt %-10.0wt %, or in the range from 2.0 wt %-9.0 wt %, or in the range from 2.5wt %-6.0 wt %, or in the range from 3.0 wt %-8.0 wt %, or in the rangefrom 3.0 wt % to 5.0 wt %, or in the range from 3.0 wt %-5.5 wt %, or inthe range from 3.5 wt %-5.0 wt %, or in the range from 3.5 wt % to 7.0wt %. It is noted that the concentration of di-adduct is expressed interms of wt % of the oligomer and not in terms of wt % in the coatingcomposition.

An illustrative reaction for synthesizing an oligomer in accordance withthe present disclosure includes reaction of a diisocyanate compound(4,4′-methylene bis(cyclohexyl isocyanate, which is also referred toherein as H12MDI) and a polyol (polypropylene glycol with M_(n)˜4000g/mol, which is also referred to herein as PPG4000) to form a polyetherurethane diisocyanate compound with formula (VI):H12MDI˜PPG4000˜H12MDI˜PPG4000˜H12MDI  (VI)where “˜” denotes a urethane linkage formed by the reaction of aterminal isocyanate group of H12MDI with a terminal alcohol group ofPPG4000 and ˜H12MDI, ˜H12MDI˜, and ˜PPG4000˜ refer to residues of H12MDIand PPG4000 remaining after the reaction. The polyether urethanediisocyanate compound has a repeat unit of the type ˜(H12MDI˜PPG4000)˜.The particular polyether urethane diisocyanate shown includes twoPPG4000 units. The reaction may also provide products having one PPG4000unit, or three or more PPG4000 units. The polyether urethanediisocyanate and any unreacted H12MDI include terminal isocyanategroups. In accordance with the present disclosure, a hydroxy acrylatecompound (such as 2-hydroxyethyl acrylate, which is referred to hereinas HEA) is included in the reaction to react with terminal isocyanategroups to convert them to terminal acrylate groups. The conversion ofterminal isocyanate groups to terminal acrylate groups effects aquenching of the isocyanate group. The amount of HEA included in thereaction may be an amount estimated to react stoichiometrically with theexpected concentration of unreacted isocyanate groups or an amount inexcess of the expected stoichiometric amount. Reaction of HEA with thepolyether urethane diisocyanate compound forms the polyether urethaneacrylate compound with formula (VII):HEA˜H12MDI˜PPG4000˜H12MDI˜PPG4000˜H12MDI  (VII)and/or the polyether urethane diacrylate compound with formula (VIII):HEA˜H12MDI˜PPG4000˜H12MDI˜PPG4000˜H12MDI˜HEA  (VIII)and reaction of HEA with unreacted H12MDI forms the di-adduct compoundwith formula (IX):HEA˜H12MDI˜HEA  (IX)where, as above, ˜ designates a urethane linkage and ˜HEA designates theresidue of HEA remaining after reaction to form the urethane linkage(consistent with formulas (IV) and (V)). The combination of a polyetherurethane diacrylate compound and a di-adduct compound in the productcomposition constitutes an oligomer in accordance with the presentdisclosure. As described more fully hereinbelow, when one or moreoligomers are used in coating compositions, coatings having improvedtear strength and critical stress characteristics result. In particular,it is demonstrated that oligomers having a high proportion of di-adductcompound provide coatings with high tear strengths and/or high criticalstress values.

Although depicted for the illustrative combination of H12MDI, HEA andPPG4000, the foregoing reaction may be generalized to an arbitrarycombination of a diisocyanate compound, a hydroxy acrylate compound, anda polyol, where the hydroxy acrylate compound reacts with terminalisocyanate groups to form terminal acrylate groups and where urethanelinkages form from reactions of isocyanate groups and alcohol groups ofthe polyol or hydroxy acrylate compound.

The oligomer includes a compound that is a polyether urethane diacrylatecompound with formula (X):(hydroxy acrylate)˜(diisocyanate˜polyol)_(x)˜diisocyanate˜(hydroxyacrylate)  (X)and a compound that is a di-adduct compound with formula (XI):(hydroxy acrylate)˜diisocyanate˜(hydroxy acrylate)  (XI)where the relative proportions of diisocyanate compound, hydroxyacrylate compound, and polyol used in the reaction to form the oligomercorrespond to the mole numbers n, m, and p disclosed hereinabove.

Compounds represented by molecular formulas (I) and (II) above, forexample, react to form a polyether urethane diisocyanate compoundrepresented by molecular formula (XII):

where y is the same as y in formula (IV) and is 1, or 2, or 3 or 4 orhigher; and x is determined by the number of repeat units of the polyol(as described hereinabove).

Further reaction of the polyether urethane isocyanate of molecularformula (VI) with the hydroxy acrylate of molecular formula (III)provides the polyether urethane diacrylate compound represented bymolecular formula (IV) referred to hereinabove and repeated below:

where y is 1, or 2, or 3, or 4 or higher; and x is determined by thenumber of repeat units of the polyol (as described hereinabove).

In an embodiment, the reaction between the diisocyanate compound,hydroxy acrylate compound, and polyol yields a series of polyetherurethane diacrylate compounds that differ in y such that the averagevalue of y over the distribution of compounds present in the finalreaction mixture is a non-integer. In an embodiment, the average valueof y in the polyether urethane diisocyanates and polyether urethanediacrylates of molecular formulas (VI) and (IV) corresponds to p or p−1(where p is as defined hereinabove). In an embodiment, the averagenumber of occurrences of the group R₁ in the polyether urethanediisocyanates and polyether urethane diacrylates of the molecularformulas (XII) and (IV) correspond to n (where n is as definedhereinabove).

The relative proportions of the polyether urethane diacrylate anddi-adduct compounds produced in the reaction are controlled by varyingthe molar ratio of the mole numbers n, m, and p. By way of illustration,the case where p=2.0 is considered. In the theoretical limit of completereaction, two equivalents p of polyol would react with three equivalentsn of a diisocyanate to form a compound having molecular formula (VI) inwhich y=2. The compound includes two terminal isocyanate groups, whichcan be quenched with subsequent addition of two equivalents m of ahydroxy acrylate compound in the theoretical limit to form thecorresponding polyether urethane diacrylate compound (IV) with y=2. Atheoretical molar ratio n:m:p=3.0:2.0:2.0 is defined for this situation.

In the foregoing exemplary theoretical limit, a reaction ofdiisocyanate, hydroxy acrylate, and polyol in the theoretical molarratio n:m:p=3.0:2.0:2.0 provides a polyether urethane diacrylatecompound having molecular formula (IV) in which y=2 without forming adi-adduct compound. Variations in the mole numbers n, m, and p providecontrol over the relative proportions of polyether urethane diacrylateand di-adduct formed in the reaction. Increasing the mole number nrelative to the mole number m or the mole number p, for example, mayincrease the amount of di-adduct compound formed in the reaction.Reaction of the diisocyanate compound, the hydroxy acrylate compound,and polyol compound in molar ratios n:m:p, where n>3.0, such as where nis between 3.0 and 4.5, m is between 1.5n-3 and 2.5n-5, and p is 2.0,for example, produce amounts of the di-adduct compound in the oligomersufficient to achieve the beneficial coating properties describedhereinbelow.

Variations in the relative proportions of di-adduct and polyetherurethane diacrylate are obtained through changes in the mole numbers n,m, and p and through such variations, it is possible to preciselycontrol the tear strength, critical stress, tensile toughness, and othermechanical properties of coatings formed from coating compositions thatinclude the oligomer. In one embodiment, control over properties isachievable by varying the number of units of polyol in the polyetherurethane diacrylate compound (e.g. p=2.0 vs. p=3.0 vs. p=4.0). Inanother embodiment, control of tear strength, tensile toughness, andother mechanical properties is achieved by varying the proportionspolyether urethane diacrylate compound and di-adduct compound. For apolyether urethane compound with a given number of polyol units,oligomers having variable proportions of di-adduct compound can beprepared. The variability in proportion of di-adduct compound can befinely controlled to provide oligomers based on a polyether urethanediacrylate compound with a fixed number of polyol units that providecoatings that offer precise or targeted values of tear strength,critical stress, tensile toughness, or other mechanical properties.

Improved fiber coatings result when utilizing a coating composition thatincorporates an oligomer that includes a polyether urethane acrylatecompound represented by molecular formula (IV) and a di-adduct compoundrepresented by molecular formula (V), where concentration of thedi-adduct compound in the oligomer is at least 1.0 wt %, or at least 1.5wt %, or at least 2.0 wt %, or at least 2.25 wt %, or at least 2.5 wt %,or at least 3.0 wt %, or at least 3.5 wt %, or at least 4.0 wt %, or atleast 4.5 wt %, or at least 5.0 wt %, or at least 7.0 wt % or at least9.0 wt %, or in the range from 1.0 wt %-10.0 wt %, or in the range from2.0 wt % to 9.0 wt %, or in the range from 3.0 wt % to 8.0 wt %, or inthe range from 3.5 wt % to 7.0 wt % or in the range from 2.5 wt % to 6.0wt %, or in the range from 3.0 wt % to 5.5 wt %, or in the range from3.5 wt % to 5.0 wt %. It is noted that the concentration of di-adduct isexpressed in terms of wt % of the oligomer and not in terms of wt % inthe coating composition. The concentration of the di-adduct compound isincreased in one embodiment by varying the molar ratio n:m:p ofdiisocyanate:hydroxy acrylate:polyol. In one aspect, molar ratios n:m:pthat are rich in diisocyanate relative to polyol promote the formationof the di-adduct compound.

In the exemplary stoichiometric ratio n:m:p=3:2:2 described hereinabove,the reaction proceeds with p equivalents of polyol, n=p+1 equivalents ofdiisocyanate, and two equivalents of hydroxy acrylate. If the molenumber n exceeds p+1, the diisocyanate compound is present in excessrelative to the amount of polyol compound needed to form the polyetherurethane acrylate of molecular formula (IV). The presence of excessdiisocyanate shifts the distribution of reaction products towardenhanced formation of the di-adduct compound.

To promote formation of the di-adduct compound from excess diisocyanatecompound, the amount of hydroxy acrylate can also be increased. For eachequivalent of diisocyanate above the stoichiometric mole number n=p+1,two equivalents of hydroxy acrylate are needed to form the di-adductcompound. In the case of arbitrary mole number p (polyol), thestoichiometric mole numbers n (diisocyanate) and m (hydroxy acrylate)are p+1 and 2, respectively. As the mole number n is increased above thestoichiometric value, the equivalents of hydroxy acrylate needed forcomplete reaction of excess diisocyanate to form the di-adduct compoundmay be expressed as m=2+2[n−(p+1)], where the leading term “2”represents the equivalents of hydroxy acrylate needed to terminate thepolyether urethane acrylate compound (compound having molecular formula(V)) and the term 2[n−(p+1)] represents the equivalents of hydroxyacrylate needed to convert the excess starting diisocyanate to thedi-adduct compound. If the actual value of the mole number m is lessthan this number of equivalents, the available hydroxy acrylate reactswith isocyanate groups present on the oligomer or free diisocyanatemolecules to form terminal acrylate groups. The relative kinetics of thetwo reaction pathways dictates the relative amounts of polyetherurethane diacrylate and di-adduct compounds formed and the deficit inhydroxy acrylate relative to the amount required to quench all unreactedisocyanate groups may be controlled to further influence the relativeproportions of polyether urethane diacrylate and di-adduct formed in thereaction.

In some embodiments, the reaction includes heating the reactioncomposition formed from the diisocyanate compound, hydroxy acrylatecompound, and polyol. The heating facilitates conversion of terminalisocyanate groups to terminal acrylate groups through a reaction of thehydroxy acrylate compound with terminal isocyanate groups. In differentembodiments, the hydroxy acrylate compound is present in excess in theinitial reaction mixture and/or is otherwise available or added inunreacted form to effect conversion of terminal isocyanate groups toterminal acrylate groups. The heating occurs at a temperature above 40°C. for at least 12 hours, or at a temperature above 40° C. for at least18 hours, or at a temperature above 40° C. for at least 24 hours, or ata temperature above 50° C. for at least 12 hours, or at a temperatureabove 50° C. for at least 18 hours, or at a temperature above 50° C. forat least 24 hours, or at a temperature above 60° C. for at least 12hours, or at a temperature above 60° C. for at least 18 hours, or at atemperature above 60° C. for at least 24 hours.

In an embodiment, conversion of terminal isocyanate groups on thepolyether urethane diacrylate compound or starting diisocyanate compound(unreacted initial amount or amount present in excess) to terminalacrylate groups is facilitated by the addition of a supplemental amountof hydroxy acrylate compound to the reaction mixture. As indicatedhereinabove, the amount of hydroxy acrylate compound needed to quench(neutralize) terminal isocyanate groups may deviate from the theoreticalnumber of equivalents due, for example, to incomplete reaction or adesire to control the relative proportions of polyether urethanediacrylate compound and di-adduct compound. As described hereinabove,once the reaction has proceeded to completion or other endpoint, it ispreferable to quench (neutralize) residual isocyanate groups to providea stabilized reaction product. In an embodiment, supplemental hydroxyacrylate is added to accomplish this objective.

In an embodiment, the amount of supplemental hydroxy acrylate compoundis in addition to the amount included in the initial reaction process.The presence of terminal isocyanate groups at any stage of the reactionis monitored, for example, by FTIR spectroscopy (e.g. using acharacteristic isocyanate stretching mode near 2265 cm′) andsupplemental hydroxy acrylate compound is added as needed until theintensity of the characteristic stretching mode of isocyanate groups isnegligible or below a pre-determined threshold. In an embodiment,supplemental hydroxy acrylate compound is added beyond the amount neededto fully convert terminal isocyanate groups to terminal acrylate groups.In different embodiments, supplemental hydroxy acrylate compound isincluded in the initial reaction mixture (as an amount above thetheoretical amount expected from the molar amounts of diisocyanate andpolyol), added as the reaction progresses, and/or added after reactionof the diisocyanate and polyol compounds has occurred to completion orpre-determined extent.

Amounts of hydroxy acrylate compound above the amount needed to fullyconvert isocyanate groups are referred to herein as excess amounts ofhydroxy acrylate compound. When added, the excess amount of hydroxyacrylate compound is at least 20% of the amount of supplemental hydroxyacrylate compound needed to fully convert terminal isocyanate groups toterminal acrylate groups, or at least 40% of the amount of supplementalhydroxy acrylate compound needed to fully convert terminal isocyanategroups to terminal acrylate groups, or at least 60% of the amount ofsupplemental hydroxy acrylate compound needed to fully convert terminalisocyanate groups to terminal acrylate groups, or at least 90% of theamount of supplemental hydroxy acrylate compound needed to fully convertterminal isocyanate groups to terminal acrylate groups.

In an embodiment, the amount of supplemental hydroxy acrylate compoundmay be sufficient to completely or nearly completely quench residualisocyanate groups present in the oligomer formed in the reaction.Quenching of isocyanate groups is desirable because isocyanate groupsare relatively unstable and often undergo reaction over time. Suchreaction alters the characteristics of the reaction composition oroligomer and may lead to inconsistencies in coatings formed therefrom.Reaction compositions and products formed from the starting diisocyanateand polyol compounds that are free of residual isocyanate groups areexpected to have greater stability and predictability ofcharacteristics.

The oligomer of the coating composition includes a polyether urethanediacrylate compound and di-adduct compound as described hereinabove. Insome aspects, the oligomer includes two or more polyether urethanediacrylate compounds and/or two or more di-adduct compounds. Theoligomer content of the coating composition includes the combinedamounts of the one or more polyether urethane diacrylate compound(s) andone or more di-adduct compound(s) and is greater than 20 wt %, orgreater than 30 wt %, or greater than 40 wt %, or in the range from 20wt %-80 wt %, or in the range from 30 wt %-70 wt %, or in the range from40 wt %-60 wt %, where the concentration of di-adduct compound withinthe oligomer content is as described above.

The curable coating composition further includes one or more monomers.The one or more monomers is/are selected to be compatible with theoligomer, to control the viscosity of the coating composition tofacilitate processing, and/or to influence the physical or chemicalproperties of the coating formed as the cured product of the coatingcomposition. The monomers include ethylenically-unsaturated compounds,ethoxylated acrylates, ethoxylated alkylphenol monoacrylates, propyleneoxide acrylates, n-propylene oxide acrylates, isopropylene oxideacrylates, monofunctional acrylates, monofunctional aliphatic epoxyacrylates, multifunctional acrylates, multifunctional aliphatic epoxyacrylates, and combinations thereof.

Representative radiation-curable ethylenically unsaturated monomersinclude alkoxylated monomers with one or more acrylate or methacrylategroups. An alkoxylated monomer is one that includes one or morealkoxylene groups, where an alkoxylene group has the form —O—R— and R isa linear or branched alkylene group. Examples of alkoxylene groupsinclude ethoxylene (—O—CH₂—CH₂—), n-propoxylene (—O—CH₂—CH₂—CH₂—),isopropoxylene (—O—CH₂—CH(CH₃)—, or —O—CH(CH₃)—CH₂—), etc. As usedherein, the degree of alkoxylation refers to the number of alkoxylenegroups in the monomer. In one embodiment, the alkoxylene groups arebonded consecutively in the monomer.

In some aspects, the coating composition includes an alkoxylated monomerof the form R₄—R₅—O—(CH(CH₃)CH₂—O)_(q)—C(O)CH═CH₂, where R₄ and R₅ arealiphatic, aromatic, or a mixture of both, and q=1 to 10, orR₄—O—(CH(CH₃)CH₂—O)_(q)—C(O)CH═CH₂, where C(O) is a carbonyl group, R₁is aliphatic or aromatic, and q=1 to 10.

Representative examples of monomers include ethylenically unsaturatedmonomers such as lauryl acrylate (e.g., SR335 available from SartomerCompany, Inc., AGEFLEX FA12 available from BASF, and PHOTOMER 4812available from IGM Resins), ethoxylated nonylphenol acrylate (e.g.,SR504 available from Sartomer Company, Inc. and PHOTOMER 4066 availablefrom IGM Resins), caprolactone acrylate (e.g., SR495 available fromSartomer Company, Inc., and TONE M-100 available from Dow Chemical),phenoxyethyl acrylate (e.g., SR339 available from Sartomer Company,Inc., AGEFLEX PEA available from BASF, and PHOTOMER 4035 available fromIGM Resins), isooctyl acrylate (e.g., SR440 available from SartomerCompany, Inc. and AGEFLEX FA8 available from BASF), tridecyl acrylate(e.g., SR489 available from Sartomer Company, Inc.), isobornyl acrylate(e.g., SR506 available from Sartomer Company, Inc. and AGEFLEX IBOAavailable from CPS Chemical Co.), tetrahydrofurfuryl acrylate (e.g.,SR285 available from Sartomer Company, Inc.), stearyl acrylate (e.g.,SR257 available from Sartomer Company, Inc.), isodecyl acrylate (e.g.,SR395 available from Sartomer Company, Inc. and AGEFLEX FA10 availablefrom BASF), 2-(2-ethoxyethoxy)ethyl acrylate (e.g., SR256 available fromSartomer Company, Inc.), epoxy acrylate (e.g., CN120, available fromSartomer Company, and EBECRYL 3201 and 3604, available from CytecIndustries Inc.), lauryloxyglycidyl acrylate (e.g., CN130 available fromSartomer Company) and phenoxyglycidyl acrylate (e.g., CN131 availablefrom Sartomer Company) and combinations thereof.

In some embodiments, the monomer component of the coating compositionincludes a multifunctional (meth)acrylate. Multifunctional ethylenicallyunsaturated monomers include multifunctional acrylate monomers andmultifunctional methacrylate monomers. Multifunctional acrylates areacrylates having two or more polymerizable acrylate moieties permolecule, or three or more polymerizable acrylate moieties per molecule.Examples of multifunctional (meth)acrylates include dipentaerythritolmonohydroxy pentaacrylate (e.g., PHOTOMER 4399 available from IGMResins); methylolpropane polyacrylates with and without alkoxylationsuch as trimethylolpropane triacrylate, ditrimethylolpropanetetraacrylate (e.g., PHOTOMER 4355, IGM Resins); alkoxylated glyceryltriacrylates such as propoxylated glyceryl triacrylate withpropoxylation being 3 or greater (e.g., PHOTOMER 4096, IGM Resins); anderythritol polyacrylates with and without alkoxylation, such aspentaerythritol tetraacrylate (e.g., SR295, available from SartomerCompany, Inc. (Westchester, Pa.)), ethoxylated pentaerythritoltetraacrylate (e.g., SR494, Sartomer Company, Inc.), dipentaerythritolpentaacrylate (e.g., PHOTOMER 4399, IGM Resins, and SR399, SartomerCompany, Inc.), tripropyleneglycol diacrylate, propoxylated hexanedioldiacrylate, tetrapropyleneglycol diacrylate, pentapropyleneglycoldiacrylate, methacrylate analogs of the foregoing, and combinationsthereof.

In some aspects, the coating composition includes an N-vinyl amidemonomer such as an N-vinyl lactam, or N-vinyl pyrrolidinone, or N-vinylcaprolactam, where the N-vinyl amide monomer is present in the coatingcomposition at a concentration greater than 1.0 wt %, or greater than2.0 wt %, or greater than 3.0 wt %, or in the range from 1.0 wt %-15.0wt %, or in the range from 2.0 wt %-10.0 wt %, or in the range from 3.0wt %-8.0 wt %.

In an embodiment, the coating composition includes one or moremonofunctional acrylate or methacrylate monomers in an amount from 5-95wt %, or from 30-75 wt %, or from 40-65 wt %. In another embodiment, thecoating composition may include one or more monofunctional aliphaticepoxy acrylate or methacrylate monomers in an amount from 5-40 wt %, orfrom 10-30 wt %.

In an embodiment, the monomer component of the coating compositionincludes a hydroxyfunctional monomer. A hydroxyfunctional monomer is amonomer that has a pendant hydroxy moiety in addition to other reactivefunctionality such as (meth)acrylate. Examples of hydroxyfunctionalmonomers including pendant hydroxyl groups include caprolactone acrylate(available from Dow Chemical as TONE M-100); poly(alkylene glycol)mono(meth)acrylates, such as poly(ethylene glycol) monoacrylate,poly(propylene glycol) monoacrylate, and poly(tetramethylene glycol)monoacrylate (each available from Monomer, Polymer & Dajac Labs);2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and4-hydroxybutyl (meth)acrylate (each available from Aldrich).

In an embodiment, the hydroxyfunctional monomer is present in an amountsufficient to improve adhesion of the coating to the optical fiber. Thehydroxyfunctional monomer is present in the coating composition in anamount between about 0.1 wt % and about 25 wt %, or in an amount betweenabout 5 wt % and about 8 wt %. The use of the hydroxyfunctional monomermay decrease the amount of adhesion promoter necessary for adequateadhesion of the primary coating to the optical fiber. The use of thehydroxyfunctional monomer may also tend to increase the hydrophilicityof the coating. Hydroxyfunctional monomers are described in more detailin U.S. Pat. No. 6,563,996, the disclosure of which is herebyincorporated by reference in its entirety.

In different embodiments, the total monomer content of the coatingcomposition is between about 5 wt % and about 95 wt %, or between about30 wt % and about 75 wt %, or between about 40 wt % and about 65 wt %.

In some embodiments, the coating composition may also include one ormore polymerization initiators and one or more additives.

The polymerization initiator facilitates initiation of thepolymerization process associated with the curing of the coatingcomposition to form the coating. Polymerization initiators includethermal initiators, chemical initiators, electron beam initiators, andphotoinitiators. Photoinitiators are preferred polymerizationinitiators. Photoinitiators include ketonic photoinitiating additivesand/or phosphine oxide additives. When used in the formation reaction ofthe coating of the present disclosure, the photoinitiator is present inan amount sufficient to enable rapid radiation curing. The wavelength ofcuring radiation is infrared, visible, or ultraviolet. Representativewavelengths include wavelengths in the range from 300 nm-1000 nm, or inthe range from 300 nm-700 nm, or in the range from 300 nm-400 nm, or inthe range from 325 nm-450 nm, or in the range from 325 nm-400 nm, or inthe range from 350 nm-400 nm. Curing can be accomplished with a lampsource (e.g. Hg lamp) or LED source (e.g. a UVLED, visible LED, orinfrared LED).

Representative photoinitiators include 1-hydroxycyclohexylphenyl ketone(e.g., IRGACURE 184 available from BASF));bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (e.g.,commercial blends IRGACURE 1800, 1850, and 1700 available from BASF);2,2-dimethoxy-2-phenylacetophenone (e.g., IRGACURE 651, available fromBASF); bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (IRGACURE 819);(2,4,6-trimethylbenzoyl)diphenyl phosphine oxide (LUCIRIN TPO, availablefrom BASF (Munich, Germany));ethoxy(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (LUCIRIN TPO-L fromBASF); and combinations thereof.

The coating composition includes a single photoinitiator or acombination of two or more photoinitiators. The total photoinitiatorconcentration in the coating composition is greater than 0.25 wt %, orgreater than 0.50 wt %, or greater than 0.75 wt %, or greater than 1.0wt %, or in the range from 0.25 wt %-5.0 wt %, or in the range from 0.50wt %-4.0 wt %, or in the range from 0.75 wt %-3.0 wt %.

In addition to monomer(s), oligomer(s), and polymerization initiator(s),the coating composition optionally includes one or more additives.Additives include an adhesion promoter, a strength additive, anantioxidant, a catalyst, a stabilizer, an optical brightener, aproperty-enhancing additive, an amine synergist, a wax, a lubricant,and/or a slip agent. Some additives operate to control thepolymerization process, thereby affecting the physical properties (e.g.,modulus, glass transition temperature) of the polymerization productformed from the coating composition. Other additives affect theintegrity of the cured product of the coating composition (e.g., protectagainst de-polymerization or oxidative degradation).

An adhesion promoter is a compound that facilitates adhesion of theprimary coating and/or primary composition to glass (e.g. the claddingportion of a glass fiber). Suitable adhesion promoters includealkoxysilanes, mercapto-functional silanes, organotitanates, andzirconates. Representative adhesion promoters include mercaptoalkylsilanes or mercaptoalkoxy silanes such as3-mercaptopropyl-trialkoxysilane (e.g.,3-mercaptopropyl-trimethoxysilane, available from Gelest (Tullytown,Pa.)); bis(trialkoxysilyl-ethyl)benzene; acryloxypropyltrialkoxysilane(e.g., (3-acryloxypropyl)-trimethoxysilane, available from Gelest),methacryloxypropyltrialkoxysilane, vinyltrialkoxysilane,bis(trialkoxysilylethyl)hexane, allyltrialkoxysilane,styrylethyltrialkoxysilane, and bis(trimethoxysilylethyl)benzene(available from United Chemical Technologies (Bristol, Pa.)); see U.S.Pat. No. 6,316,516, the disclosure of which is hereby incorporated byreference in its entirety herein.

The adhesion promoter is present in the coating composition in an amountbetween 0.02 wt % and 10.0 wt %, or between 0.05 wt % and 4.0 wt %, orbetween 0.1 wt % and 4.0 wt %, or between 0.1 wt % and 3.0 wt %, orbetween 0.1 wt % and 2.0 wt %, or between 0.1 wt % and 1.0 wt %, orbetween 0.5 wt % and 4.0 wt %, or between 0.5 wt % and 3.0 wt %, orbetween 0.5 wt % and 2.0 wt %, or between 0.5 wt % to 1.0 wt %.

A representative antioxidant is thiodiethylenebis[3-(3,5-di-tert-butyl)-4-hydroxy-phenyl) propionate] (e.g., IRGANOX1035, available from BASF). In some aspects, an antioxidant is presentin the coating composition in an amount greater than 0.25 wt %, orgreater than 0.50 wt %, or greater than 0.75 wt %, or greater than 1.0wt %, or an amount in the range from 0.25 wt %-3.0 wt %, or an amount inthe range from 0.50 wt %-2.0 wt %, or an amount in the range from 0.75wt %-1.5 wt %.

Representative optical brighteners include TINOPAL OB (available fromBASF); Blankophor KLA (available from Bayer); bisbenzoxazole compounds;phenylcoumarin compounds; and bis(styryl)biphenyl compounds. In anembodiment, the optical brightener is present in the coating compositionat a concentration of 0.005 wt %-0.3 wt %.

Representative amine synergists include triethanolamine;1,4-diazabicyclo[2.2.2]octane (DABCO), triethylamine, andmethyldiethanolamine. In an embodiment, an amine synergist is present ata concentration of 0.02 wt %-0.5 wt %.

Curing of the coating composition provides a cured product, such as aprimary coating, with increased resistance to defect formation duringmanufacturing or subsequent processing, including splicing.

As described in greater detail hereinbelow, the present disclosuredemonstrates that primary coatings having low pullout force and strongcohesion can be stripped cleanly from glass fibers while maintainingresistance to defect formation during splicing. The primary coatings ofthe present disclosure combine a low Young's modulus with strongcohesion to enable splicing of fibers and ribbons with minimal coatingresidue on the spliced portion of the optical fiber and few defects inthe coating remaining on the unspliced portion of the optical fiber.

In a continuous optical fiber manufacturing process, a glass fiber isdrawn from a heated preform and sized to a target diameter (typically125 μm). The glass fiber is then cooled and directed to a coating systemthat applies a liquid primary coating composition to the glass fiber.Two process options are viable after application of the liquid primarycoating composition to the glass fiber. In one process option(wet-on-dry process), the liquid primary coating composition is cured toform a solidified primary coating, the liquid secondary coatingcomposition is applied to the cured primary coating, and the liquidsecondary coating composition is cured to form a solidified secondarycoating. In a second process option (wet-on-wet process), the liquidsecondary coating composition is applied to the liquid primary coatingcomposition, and both liquid coating compositions are curedsimultaneously to provide solidified primary and secondary coatings. Insome processes, the coating system further applies a tertiary coating tothe secondary coating. Typically, the tertiary coating is an ink layerused to mark the fiber for identification purposes. After the fiberexits the coating system, the fiber is collected and stored at roomtemperature. Collection of the fiber typically entails winding the fiberon a spool and storing the spool.

To improve process efficiency, it is desirable to increase the drawspeed of the fiber along the process pathway extending from the preformto the collection point. As the draw speed increases, however, the curespeed of coating compositions must increase. The coating compositionsdisclosed herein are compatible with fiber draw processes that operateat a draw speed greater than 35 m/s, or greater than 40 m/s, or greaterthan 45 m/s, or greater than 50 m/s, or greater than 55 m/s.

In the course of the present disclosure, it has been observed thatpullout force is a reliable indicator of the adhesion of a primarycoating to a glass fiber. Adhesion of the primary coating to a glassfiber needs to be strong enough to prevent separation of the primarycoating from the glass fiber during routine handling, but not so strongthat it is difficult to remove the primary coating during the strippingand splicing operations.

The primary coatings disclosed herein exhibit a pullout force consistentwith the level of adhesion needed for adherence to a glass fiber whilepermitting removal without residue during stripping. In the course ofthe present disclosure, however, it has been observed that the pulloutforce of primary coatings evolves over time. In particular, the pulloutforce increases from an initial value at the time of draw to highervalues at later times. Time evolution of pullout force is undesirable.As pullout force increases over time, adhesion of the primary coating tothe glass fiber becomes stronger and it becomes more difficult to removethe primary coating during splicing without leaving residue on thestripped portion of the fiber.

The pullout force of the primary coatings disclosed herein exhibitsimproved stability over time relative to prior art primary coatings. Forpurposes of the present disclosure, stability over time is measuredbeginning from the time the fiber is stored after coating in themanufacturing process used to make the fiber from a preform. The stateof the optical fiber at the initial time of storage in the originalmanufacturing process is referred herein as the “as-drawn state” of theoptical fiber. In the as-drawn state, the fiber is coated and at roomtemperature on a storage device (e.g. spool) positioned along acontinuous process pathway extending from the preform through a coatingsystem to the storage device. The time of placement of the fiber in theas-drawn state is the time at which the fiber is collected at thestorage device. Measurements of the properties of the fiber in theas-drawn state are made as soon as practicable following time ofcollection at the storage device. In instances in which a measurementdelay occurs, the properties of the fiber in the as-drawn state can bedetermined from data obtained at later times through back extrapolationof a fit obtained from Eq. (3) given below.

Cohesion refers to tear strength and/or tensile toughness. Tensiletoughness is a measure of the force needed to initiate a break in acoating and tear strength is a measure of the force required to expand abreak in a coating once it has been initiated.

The present disclosure extends to optical fibers coated with the curedproduct of the coating compositions. The optical fiber includes a glasswaveguide with a higher index glass core region surrounded by a lowerindex glass cladding region. A coating formed as a cured product of thepresent coating compositions surrounds and is in direct contact with theglass cladding. The cured product of the present coating compositionspreferably functions as the primary coating of the fiber. The fiber mayinclude a secondary coating or both a secondary and tertiary coating.

Examples

Several illustrative coatings prepared from coating compositions thatincluded an oligomer in accordance with the present disclosure wereprepared and tested. The tests included measurements of pullout force,tear strength, and tensile toughness. The preparation of oligomers,description of the components of the coating compositions, processingconditions used to form oligomers and coatings, test methodologies, andtest results are described hereinbelow.

Coating Compositions.

The components of coating compositions and the concentrations of eachcomponent are summarized in Table 1. The coating compositions A and Blisted in Table 1 are in accordance with the present disclosure. Coatingcomposition C is a comparative composition. Additional commercialcoating compositions designated as D, E, F, and G were tested forcomparative purposes. The commercial compositions were obtained from DSMDesotech (Elgin, Ill.) and included conventional oligomers. The specificformulations are proprietary to the vendor. Composition D had productcode 950-076, Composition E had product code 950-030, Composition G hadproduct code 3741-143, and Composition F was a variant of Composition Gthat included an adhesion promoter. The oligomers present in comparativecoating compositions C-G contained a lower concentration of di-adductcompound than coating compositions A and B.

TABLE 1 Coating Formulations Formulation Component A B C Oligomer 1 (wt%) 49.10 Oligomer 2 (wt %) 49.10 Oligomer 3 (wt %) 50.0 SR504 (wt %)45.66 45.66 46.5 NVC (wt %) 1.96 1.96 2.0 TPO (wt %) 1.47 1.47 1.5Irganox 1035 (wt %) 0.98 0.98 1.0 3-mercaptopropyltrimethoxysilane (wt%) 0.79 3-acryloxypropyltrimethoxysilane (wt %) 0.79 0.8 Tetrathiol (wt%) 0.03 0.03 0.03

Oligomer 1 and Oligomer 2 are products of reactions of H12MDI(4,4′-methylene bis(cyclohexyl isocyanate), PPG4000 (polypropyleneglycol with M_(n)˜4000 g/mol) and HEA (2-hydroxyethyl acrylate). Thereaction conditions are described below. SR504 isethoxylated(4)nonylphenol acrylate (available from Sartomer). NVC isN-vinylcaprolactam (available from ISP Technologies). TPO is(2,4,6-trimethylbenzoyl)diphenyl phosphine oxide (available from BASFunder the trade name Lucirin) and functions as a photoinitiator. Irganox1035 is thiodiethylene bis[3-(3,5-di-tert-butyl)-4-hydroxy-phenyl)propionate] (available from BASF under the trade name Irganox 1035) andfunctions as an antioxidant. 3-acryloxypropyl trimethoxysilane(available from Gelest) and 3-mercaptopropyl trimethoxysilane (availablefrom Aldrich) are adhesion promoters. Tetrathiol ispentaerythritoltetrakis(3-mercaptopropionate) (available from Aldrich)and functions as a quencher of residual dibutyltin dilaurate catalystthat may be present in Oligomer 1 and Oligomer 2.

Oligomer 1 and Oligomer 2.

Coating compositions A and B are curable coating compositions thatincluded an oligomer of the type disclosed herein. For purposes ofillustration, preparation of exemplary oligomers from H12MDI(4,4′-methylene bis(cyclohexyl isocyanate), PPG4000 (polypropyleneglycol with M_(n)˜4000 g/mol) and HEA (2-hydroxyethyl acrylate) inaccordance with the reaction scheme disclosed hereinabove is described.All reagents were used as supplied by the manufacturer and were notsubjected to further purification. H12MDI was obtained from ALDRICH.PPG4000 was obtained from COVESTRO and was certified to have anunsaturation of 0.004 meq/g as determined by the method described in thestandard ASTM D4671-16. HEA was obtained from KOWA.

The relative amounts of the reactants and reaction conditions werevaried to obtain Oligomer 1 and Oligomer 2. Oligomer 1 and Oligomer 2were prepared with different initial molar ratios of reactants with themolar ratios of the reactants satisfying the ratioH12MDI:HEA:PPG4000=n:m:p, where n was in the range from 3.0 to 4.0, mwas in the range from 1.5n-3 to 2.5n-5, and p=2. In the reactions usedto form Oligomer 1 and Oligomer 2, dibutyltin dilaurate was used as acatalyst (at a level of 160 ppm based on the mass of the initialreaction mixture) and 2,6-di-tert-butyl-4-methylphenol (BHT) was used asan inhibitor (at a level of 400 ppm based on the mass of the initialreaction mixture).

The amounts of the reactants used to prepare Oligomer 1 and Oligomer 2are summarized in Table 2 below. Corresponding sample numbers will beused herein to refer to coating compositions and cured films formed fromcoating compositions that individually contain each of the sixoligomers. The corresponding mole numbers used in the preparation ofeach of the six samples are listed in Table 3 below. The mole numbersare normalized to set the mole number p of PPG4000 to 2.0.

TABLE 2 Reactants and Amounts for Oligomers Oligomer H12MDI (g) HEA (g)PPG4000 (g) 1 26.1 10.6 213.3 2 26.1 10.6 213.3

TABLE 3 Mole Numbers and Di-adduct Content for Oligomers H12MDI HEAPPG4000 Mole Number Mole Number Mole Number Di-adduct Sample (n) (m) (p)(wt %) 1 3.7 3.4 2.0 3.7 2 3.7 3.4 2.0 3.7

Oligomer 1 and Oligomer 2 were prepared by mixing 4,4′-methylenebis(cyclohexyl isocyanate), dibutyltin dilaurate and 2,6-di-tert-butyl-4methylphenol at room temperature in a 500 mL flask. The 500 mL flask wasequipped with a thermometer, a CaCl₂) drying tube, and a stirrer. Whilecontinuously stirring the contents of the flask, PPG4000 was added overa time period of 30-40 minutes using an addition funnel. The internaltemperature of the reaction mixture was monitored as the PPG4000 wasadded and the introduction of PPG4000 was controlled to prevent excessheating (arising from the exothermic nature of the reaction). After thePPG4000 was added, the reaction mixture was heated in an oil bath atabout 70° C.-75° C. for about 1-1½ hours. At various intervals, samplesof the reaction mixture were retrieved for analysis by infraredspectroscopy (FTIR) to monitor the progress of the reaction bydetermining the concentration of unreacted isocyanate groups. Theconcentration of unreacted isocyanate groups was assessed based on theintensity of a characteristic isocyanate stretching mode near 2265 cm⁻¹.The flask was removed from the oil bath and its contents were allowed tocool to below 65° C. Addition of supplemental HEA was conducted toinsure complete quenching of isocyanate groups. The supplemental HEA wasadded dropwise over 2-5 minutes using an addition funnel. After additionof the supplemental HEA, the flask was returned to the oil bath and itscontents were again heated to about 70° C.-75° C. for about 1-1½ hours.FTIR analysis was conducted on the reaction mixture to assess thepresence of isocyanate groups and the process was repeated until enoughsupplemental HEA was added to fully react any unreacted isocyanategroups. The reaction was deemed complete when no appreciable isocyanatestretching intensity was detected in the FTIR measurement. The HEAamounts listed in Table 1 include the initial amount of HEA in thecomposition and any amount of supplemental HEA needed to quenchunreacted isocyanate groups.

The concentration (wt %) of di-adduct compound was determined by gelpermeation chromatography (GPC). A Waters Alliance 2690 GPC instrumentwas used to determine the di-adduct concentration. The mobile phase wasTHF. The instrument included a series of three Polymer Labs columns.Each column had a length of 300 mm and an inside diameter of 7.5 mm. Twoof the columns (columns 1 and 2) were sold under Part No. PL1110-6504 byAgilent Technologies and were packed with PLgel Mixed D stationary phase(polystyrene divinyl benzene copolymer, average particle size=5 μm,specified molecular weight range=200-400,000 g/mol). The third column(column 3) was sold under Part No. PL1110-6520 by Agilent Technologiesand was packed with PLgel 100A stationary phase (polystyrene divinylbenzene copolymer, average particle size=5 μm, specified molecularweight range=up to 4,000 g/mol). The columns were calibrated withpolystyrene standards ranging from 162-6,980,000 g/mol using EasiCalPS-1 & 2 polymer calibrant kits (Agilent Technologies Part Nos.PL2010-505 and PL2010-0601). The GPC instrument was operated under thefollowing conditions: flow rate=1.0 mL/min, column temperature=40° C.,injection volume=100 μL, and run time=35 min (isocratic conditions). Thedetector was a Waters Alliance 2410 differential refractometer operatedat 40° C. and sensitivity level 4. The samples were injected twice alongwith a THF+0.05% toluene blank.

The amount (wt %) of di-adduct in Oligomer 1 and Oligomer 2 wasquantified using the preceding GPC system and technique. A calibrationcurve was obtained using standard solutions containing known amounts ofthe di-adduct compound (HEA-H12MDI-REA) in THF. Standard solutions withdi-adduct concentrations of 115.2 μg/g, 462.6 μg/g, 825.1 μg/g, and 4180μg/g were prepared. (As used herein, the dimension “μg/g” refers to μgof di-adduct per gram of total solution (di-adduct+THF)). Two 100 μLaliquots of each di-adduct standard solution were injected into thecolumn to obtain the calibration curve. The retention time of thedi-adduct was approximately 23 min and the area of the GPC peak of thedi-adduct was measured and correlated with di-adduct concentration. Alinear correlation of peak area as a function of di-adduct concentrationwas obtained (correlation coefficient (R²)=0.999564).

The di-adduct concentration in Oligomer 1 and Oligomer 2 was determinedusing the calibration. Samples were prepared by diluting ˜0.10 g of eacholigomer in THF to obtain a ˜1.5 g test solution. The test solution wasrun through the GPC instrument and the area of the peak associated withthe di-adduct compound was determined. The di-adduct concentration inunits of μgig was obtained from the peak area and the calibration curve,and was converted to wt % by multiplying by the weight (g) of the testsolution and dividing by the weight of the sample of oligomer beforedilution with THF. The wt % of di-adduct compound present in Oligomer 1and Oligomer 2 are reported in Table 3. The entries in Table 1 forOligomer 1 and Oligomer 2 include the combined amount of polyetherurethane acrylate compound and di-adduct compound.

Through variation in the relative mole ratios of H12MDI, HEA, andPPG4000, the illustrative oligomers include a polyether urethanecompound of the type shown in molecular formula (IV) hereinabove and anenhanced concentration of di-adduct compound of the type shown inmolecular formula (V) hereinabove. As described more fully hereinbelow,coatings formed using oligomers that contain the di-adduct compound inamounts of at least 2.50 wt % have significantly improved pullout force,tear strength and/or tensile toughness (relative to coatings formed frompolyether urethane acrylate compounds alone or polyether urethaneacrylate compounds combined with lesser amounts of di-adduct compound)while maintaining a favorable Young's modulus for primary coatings ofoptical fibers.

Oligomer 3.

Oligomer 3 is a commercial oligomer (obtained from Dymax (product codeBR3741). Oligomer 3 was prepared from starting materials similar tothose used for Oligomer 1 and Oligomer 2. The ratio n:m:p used in thepreparation of Oligomer 3, however, produced a smaller concentration ofdi-adduct compound.

Preparation of Coating Compositions.

The coating compositions of Table 1 were each formulated using ahigh-speed mixer in an appropriate container heated to 60° C., with aheating band or heating mantle. In each case, the components wereweighed into the container using a balance and allowed to mix until thesolid components were thoroughly dissolved and the mixture appearedhomogeneous. The oligomer and monomers (SR504, NVC) of each compositionwere blended together for at least 10 minutes at 55° C.-60° C. Thephotoinitiator, antioxidant, and catalyst quencher were then added, andblending was continued for one hour while maintaining a temperature of55° C.-60° C. Finally, the adhesion promoter was added, and blending wascontinued for 30 minutes at 55° C.-60° C. to form the coatingcompositions. Comparative coating compositions D-G were formulated bythe vendor and used as received.

Various properties of cured products formed by curing the coatingcompositions were measured. A discussion of curing conditions, sampleconfiguration and properties follows.

Young's Modulus and Tensile Toughness.

Young's modulus (E) was measured on films formed by the curing coatingcompositions A, B, and C. Separate films were formed from each coatingcomposition. Wet films of the coating composition were cast on siliconerelease paper with the aid of a draw-down box having a gap thickness ofabout 0.005″. The wet films were cured with a UV dose of 1.2 J/cm²(measured over a wavelength range of 225-424 nm by a Light Bug modelIL490 from International Light) by a Fusion Systems UV curing apparatuswith a 600 W/in D-bulb (50% Power and approximately 12 ft/min beltspeed) to yield cured coatings in film form. Cured film thickness wasbetween about 0.0030″ and 0.0035″.

The films were aged (23° C., 50% relative humidity) for at least 16hours prior to testing. Film samples were cut to dimensions of 12.5cm×13 mm using a cutting template and a scalpel. Young's modulus,tensile strength at break, and % elongation (% strain at break) weremeasured at room temperature (approximately 20° C.) on the film samplesusing a MTS Sintech tensile test instrument following procedures setforth in ASTM Standard D882-97. Young's modulus is defined as thesteepest slope of the beginning of the stress-strain curve. Tensiletoughness is defined as the integrated area under the stress-straincurve. Films were tested at an elongation rate of 2.5 cm/min with theinitial gauge length of 5.1 cm.

Tear Strength.

Tear strength of films formed from coating compositions A-C wasmeasured. Tear strength (G_(c)) is related to the force required tobreak the coating when the coating is under tension. The tear strengthis calculated from Eq. (1):

$\begin{matrix}{G_{c} = \frac{\left( {\frac{F_{break}}{B \cdot d} \cdot C \cdot \sqrt{\pi\frac{b}{2}}} \right)^{2}}{S}} & (1)\end{matrix}$where F_(break) is the force at break, b is the slit length, d is thefilm thickness, B is the width of the test piece. B and b are instrumentparameters with values given below. S is the segment modulus calculatedfrom the stresses at elongations of 0.05% and 2%, and C is a samplegeometry factor defined as follows for the technique used herein todetermine tear strength:

$\begin{matrix}{C = \sqrt{\frac{1}{\cos\left( \frac{\pi\; b}{2B} \right)}}} & (2)\end{matrix}$

Tear strength (G_(c)) was measured at room temperature (approximately20° C.) with a MTS Sintech tensile tester. Each coating compositionmeasured was cast on a glass plate with the aid of a draw-down boxhaving a gap thickness of about 0.005″ and immediately cured under UVirradiation using a dose of 1 J/cm². The shape and dimensions of thecured films were prepared according to the International Standard ISO816 (second edition 1983-12-01) “Determination of tear strength of smalltest pieces (Delft test pieces)”. The cured films were conditioned at23° C.±2° C. and 50% relative humidity (RH) for at least 16 hours. Theinitial gauge length was 5.0 cm and test speed was set at 0.1 mm/min.Three to five specimens of each film were tested. Tear strength (G_(e))was calculated from Eqs. (1) and (2). For the test instrument used inthe measurements, slit length b was 5.0 mm, width B of the test piecewas 9.0 mm, and sample geometry factor C was 1.247.

Pullout Force.

Pullout force was measured at room temperature (approximately 20° C.) onsamples of glass fibers coated with each of the coating compositionsA-G. Separate glass fibers (diameter 125 μm) were coated with each ofthe coating compositions A-G. The coating compositions were cured withmercury lamps to form primary coatings on the glass fiber. The thicknessof the primary coating was 32.5 μm. The primary coating surrounded andwas in direct contact with the glass fiber. The fiber samples alsoincluded a secondary coating with a thickness of 26 μm and a Young'smodulus of 1600 MPa. The secondary coatings were formed by applying asecondary coating composition to the (cured) primary coating and curingthe secondary coating composition with mercury lamps to form a secondarycoating. The secondary coating surrounded and was in direct contact withthe primary coating.

The pullout force test measures the peak force needed to pull a 1 cmlength of glass fiber out of a surrounding coating. To perform the test,the coating at each end of the coated fiber was fixed (glued) toseparate support surfaces made with a 1 square inch tab of heavy stockpaper. The one end of the fiber sample was cut at a distance of 1 cmfrom the support surface and nicked at the interface with the supportsurface. The glass fiber was then pulled out of the coating by pullingthe two tabs apart and the peak force was determined. The peak force isa measure of the strength of adhesion of the coating to the glass fiber.Additional details of the test procedure follow.

Pullout force measurements were made on fiber samples with a length offive inches. Each end of the fiber sample was glued to a 1″×1″ paper tab(heavy stock, comparable to a manila folder). Each end of the fibersample was oriented perpendicular to an edge of a paper tab and a stripof glue extending a distance of 0.625 inches from the center of the edgetoward the center of the tab was applied. The fiber sample was placed onthe glue with a portion of the fiber extending slightly beyond the glue.The glue was allowed to dry (about 30 min). The fiber sample was thenconditioned in a controlled environment (room temperature and ˜50%relative humidity) for at least two hours. A gauge length (1 cm) wasdefined by cutting the coating at one end of the fiber sample at aposition 1 cm from the edge of the tab. The cut extended through thefiber and glue to the tab. The fiber sample was then turned over and thecoating of the cut end of the fiber sample was nicked at the edge of thetab. After nicking, the fiber sample was oriented vertically and thetabs were inserted into upper and lower pneumatic grips of a universaltensile machine equipped with a 5 lb load cell (Instron instrument). Thetab with the nicked end of the fiber was inserted into the upper grip.The grips were closed and pulled apart at a rate of 5 mm/min until theglass fiber was separated from the coating (approximately two minutes).The force applied was measured as a function of time and recorded toprovide a force curve (force as a function of time). Pullout force wasdefined to be the peak force observed during the pullout test. Thepullout force measurements were completed at room temperature.

A representative schematic force curve is shown in FIG. 3. The force wasobserved to initially increase with time to a peak value and thendecreased. The pullout force is the peak force. The decrease in forcefollowing the peak force is associated with the frictional force ofsliding the coating along the glass fiber. As the coating slides fromthe glass fiber, the contact area of the coating with the fiberdecreases and a commensurate decrease in force is observed. When thecoating is fully removed from the glass fiber, the force drops to zero.

Results.

The Young's modulus (E), tear strength (G_(c)), and tensile toughnessfor cured film samples of coating compositions A-C, and the pulloutforce results for fiber samples coated with cured products of coatingcompositions A-G are summarized in Table 4. The pullout forcecorresponds to pullout force of fiber samples in the as-drawn statedescribed above.

TABLE 4 Properties of Cured Coating Compositions Young's Tensile PulloutModulus (E) Tear Strength Toughness Force (MPa) (G_(c)) (J/m²) (kJ/m³)(lb_(f)/cm) A 0.57 56.1 0.9 B 1.0 47.6 0.9 C 0.70 29.0 407 1.0 D 3.0 E2.8 F 1.9 G 2.0

The Young's modulus (E) of the present coatings have a Young's modulus(E) of less than 1.0 MPa, or less than 0.8 MPa, or less than 0.7 MPa, orless than 0.6 MPa, or less than 0.5 MPa, or in the range from 0.1MPa-1.0 MPa, or in the range from 0.3 MPa-1.0 MPa, or in the range from0.45 MPa-1.0 MPa, or in the range from 0.2 MPa-0.9 MPa, or in the rangefrom 0.3 MPa-0.8 MPa, where Young's modulus (E) is determined accordingto the procedure described herein.

The tear strength (G_(c)) of the present coatings is at least 30 J/m²,or at least 35 J/m², or at least 40 J/m², or at least 45 J/m², or atleast 50 J/m², or at least 55 J/m², or in the range from 30 J/m²-70J/m², or in the range from 35 J/m²-65 J/m², or in the range from 40J/m²-60 J/m², where tear strength (G_(c)) is determined according to theprocedure described herein.

The tensile toughness of the present coatings is greater than 500 kJ/m³,or greater than 600 kJ/m³, or greater than 700 kJ/m³, or greater than800 kJ/m³, or in the range from 500 kJ/m³ to 1200 kJ/m³, or in the rangefrom 600 kJ/m³ to 1100 kJ/m³, or in the range from 700 kJ/m³ to 1000kJ/m³, where tensile toughness is determined according to the proceduredescribed herein.

In various embodiments, coatings or cured products prepared from acoating composition that includes an oligomer in accordance with thepresent disclosure have a Young's modulus of less than 1.0 MPa with atear strength of at least 35 J/m², or a Young's modulus of less than 0.8MPa with a tear strength of at least 35 J/m², or a Young's modulus ofless than 0.6 MPa with a tear strength of at least 35 J/m², or a Young'smodulus of less than 0.5 MPa with a tear strength of at least 35 J/m²,or a Young's modulus of less than 1.0 MPa with a tear strength of atleast 45 J/m², or a Young's modulus of less than 0.8 MPa with a tearstrength of at least 45 J/m², or a Young's modulus of less than 0.6 MPawith a tear strength of at least 45 J/m², or a Young's modulus of lessthan 0.5 MPa with a tear strength of at least 45 J/m², or a Young'smodulus of less than 1.0 MPa with a tear strength of at least 55 J/m²,or a Young's modulus of less than 0.8 MPa with a tear strength of atleast 55 J/m², or a Young's modulus of less than 0.6 MPa with a tearstrength of at least 55 J/m², or a Young's modulus of less than 0.5 MPawith a tear strength of at least 55 J/m², where tear strength andYoung's modulus are determined according to the procedure describedherein.

In various embodiments, coatings or cured products prepared from acoating composition that includes an oligomer in accordance with thepresent disclosure have a Young's modulus in the range from 0.1 MPa-1.0MPa with a tear strength in the range from 35 J/m²-75 J/m², or a Young'smodulus in the range from 0.45 MPa-1.0 MPa with a tear strength in therange from 35 J/m²-75 J/m², or a Young's modulus in the range from 0.3MPa-0.8 MPa with a tear strength in the range from 35 J/m²-75 J/m², or aYoung's modulus in the range from 0.1 MPa-1.0 MPa with a tear strengthin the range from 45 J/m²-70 J/m², or a Young's modulus in the rangefrom 0.45 MPa-1.0 MPa with a tear strength in the range from 45 J/m²-70J/m², or a Young's modulus in the range from 0.3 MPa-0.8 MPa with a tearstrength in the range from 45 J/m²-70 J/m², or a Young's modulus in therange from 0.1 MPa-1.0 MPa with a tear strength in the range from 50J/m²-65 J/m², or a Young's modulus in the range from 0.45 MPa-1.0 MPawith a tear strength in the range from 50 J/m²-65 J/m², or a Young'smodulus in the range from 0.3 MPa-0.8 MPa with a tear strength in therange from 50 J/m²-65 J/m², where tear strength and Young's modulus aredetermined according to the procedure described herein.

FIGS. 4-8 show the time dependence of the pullout force at roomtemperature (approximately 20° C.) for fiber samples coated with curedproducts of compositions A-G. Time=0 days corresponds to fiber samplesin the as-drawn state described above. The results indicate that pulloutforce increases as the fiber sample ages and approaches an asymptoticlimit at long aging times. The aging behavior can be modeled with Eq.(3):

$\begin{matrix}{\frac{{P(t)} - P_{0}}{P_{Aged} - P_{0}} = {1 - {\exp\left( {- {kt}} \right)}}} & (3)\end{matrix}$where t is time in days, P(t) is pullout force at time t, P₀ is thepullout force of the fiber sample in the as-drawn state, P_(Aged) is theasymptotic limit of pullout force, and k is a time constant. Fits of themodel to data is shown in FIGS. 4-6 and yield an approximate timeconstant k=0.15/day.

The results shown in FIGS. 4 and 5 indicate that coating compositions Aand B provide primary coatings for fiber samples with both a low pulloutforce in the as-drawn state and a small increase in pullout force overtime as the fiber sample ages. The low pullout force in the as-drawnstate indicates that adhesion of the primary coating to the glass fiberis adequate to retain the coating on the glass fiber while permittingremoval of the coating without leaving residue during a strippingoperation. The small increase in pullout force over time indicates thatthe adhesion properties remain stable and that the coating can becleanly removed from the fiber over extended periods of time. Thecoating derived from comparative coating composition C exhibits a lowpullout force for fiber samples in the as-drawn state, but a largeincrease in pullout force as the fiber sample ages (FIG. 6). The largeincrease in pullout force over time indicates a greater tendency forresidue to remain on the fiber during stripping if the fiber is storedfor an extended period of time before the stripping operation. Coatingsderived from comparative coating compositions D-G show small increasesin pullout force over time as the fiber sample ages, but exhibit largepullout forces for fiber samples in the as-drawn state (FIGS. 7-8). Thelarge pullout force in the as-drawn state indicates that the fibercannot be cleanly stripped and the increase in pullout force over timeindicates that the problem becomes more severe over time.

In the course of the present disclosure, it has been determined in oneaspect that a primary coating can be stripped cleanly from a glass fiberif the pullout force of a primary coating is less than 1.7 lb_(f)/cmwhen the fiber is in the as-drawn state and the pullout force increasesby less than a factor of 2.0 at room temperature over a time period of60 or more days beginning from the time the fiber is placed in theas-drawn state, where pullout force is determined according to theprocedure described herein.

In one aspect, the pullout force of the primary coatings disclosedherein is less than 1.7 lb_(f)/cm when the fiber is in the as-drawnstate and increases by less than a factor of 2.0 over a time period of60 or more days beginning from the time the fiber is placed in theas-drawn state. In another aspect, the pullout force of the primarycoatings disclosed herein is less than 1.7 lb_(f)/cm when the fiber isin the as-drawn state and increases by less than a factor of 1.9 over atime period of 60 or more days beginning from the time the fiber isplaced in the as-drawn state. In a further aspect, the pullout force ofthe primary coatings disclosed herein is less than 1.7 lb_(f)/cm whenthe fiber is in the as-drawn state and increases by less than a factorof 1.8 over a time period of 60 or more days beginning from the time thefiber is placed in the as-drawn state. In the foregoing, pullout forceis determined according to the procedure described herein.

In one aspect, the pullout force of the primary coatings disclosedherein is less than 1.5 lb_(f)/cm when the fiber is in the as-drawnstate and increases by less than a factor of 2.0 over a time period of60 or more days beginning from the time the fiber is placed in theas-drawn state. In another aspect, the pullout force of the primarycoatings disclosed herein is less than 1.5 lb_(f)/cm when the fiber isin the as-drawn state and increases by less than a factor of 1.9 over atime period of 60 or more days beginning from the time the fiber isplaced in the as-drawn state. In a further aspect, the pullout force ofthe primary coatings disclosed herein is less than 1.5 lb_(f)/cm whenthe fiber is in the as-drawn state and increases by less than a factorof 1.8 over a time period of 60 or more days beginning from the time thefiber is placed in the as-drawn state. In the foregoing, pullout forceis determined according to the procedure described herein.

In one aspect, the pullout force of the primary coatings disclosedherein is less than 1.3 lb_(f)/cm when the fiber is in the as-drawnstate and increases by less than a factor of 2.0 over a time period of60 or more days beginning from the time the fiber is placed in theas-drawn state. In another aspect, the pullout force of the primarycoatings disclosed herein is less than 1.3 lb_(f)/cm when the fiber isin the as-drawn state and increases by less than a factor of 1.9 over atime period of 60 or more days beginning from the time the fiber isplaced in the as-drawn state. In a further aspect, the pullout force ofthe primary coatings disclosed herein is less than 1.3 lb_(f)/cm whenthe fiber is in the as-drawn state and increases by less than a factorof 1.8 over a time period of 60 or more days beginning from the time thefiber is placed in the as-drawn state. In the foregoing, pullout forceis determined according to the procedure described herein.

In one aspect, the pullout force of the primary coatings disclosedherein is less than 1.1 lb_(f)/cm when the fiber is in the as-drawnstate and increases by less than a factor of 2.0 over a time period of60 or more days beginning from the time the fiber is placed in theas-drawn state. In another aspect, the pullout force of the primarycoatings disclosed herein is less than 1.1 lb_(f)/cm when the fiber isin the as-drawn state and increases by less than a factor of 1.9 over atime period of 60 or more days beginning from the time the fiber isplaced in the as-drawn state. In a further aspect, the pullout force ofthe primary coatings disclosed herein is less than 1.1 lb_(f)/cm whenthe fiber is in the as-drawn state and increases by less than a factorof 1.8 over a time period of 60 or more days beginning from the time thefiber is placed in the as-drawn state. In the foregoing, pullout forceis determined according to the procedure described herein.

The pullout force of the present coatings, when configured as a primarycoating with a thickness of 32.5 μm on a glass fiber having a diameterof 125 μm and surrounded by a secondary coating with a thickness of 26μm and Young's modulus of 1600 MPa in the as-drawn state, is less than1.8 lb_(f), or less than 1.6 lb_(f), or less than 1.5 lb_(f), or lessthan 1.4 lb_(f), or less than 1.3 lb_(f), or in the range from 1.2lb_(f) to 1.8 lb_(f), or in the range from 1.3 lb_(f) to 1.7 lb_(f), orin the range from 1.4 lb_(f) to 1.6 lb_(f), where pullout force isdetermined according to the procedure described herein.

Clause 1 of the description discloses:

A coating for optical fibers comprising:

-   -   a Young's modulus less than 1.0 MPa; and    -   a pullout force less than 1.7 lb_(f)/cm when configured with        thickness 32.5 μm to surround and directly contact a glass fiber        having a diameter of 125 μm in an as-drawn state, said pullout        force increasing by less than a factor of 2.0 upon aging said        coating on said glass fiber for at least 60 days.

Clause 2 of the description discloses:

The coating of clause 1, wherein said Young's modulus is less than 0.8MPa.

Clause 3 of the description discloses:

The coating of clause 1, wherein said Young's modulus is less than 0.6MPa.

Clause 4 of the description discloses:

The coating of any of clauses 1-3, wherein said pullout force is lessthan 1.5 lb_(f)/cm.

Clause 5 of the description discloses:

The coating of any of clauses 1-3, wherein said pullout force is lessthan 1.3 lb_(f)/cm.

Clause 6 of the description discloses:

The coating of any of clauses 1-5, wherein said pullout force increasesby less than a factor of 1.9 upon aging said coating on said glass fiberfor at least 60 days.

Clause 7 of the description discloses:

The coating of any of clauses 1-5, wherein said pullout force increasesby less than a factor of 1.8 upon aging said coating on said glass fiberfor at least 60 days.

Clause 8 of the description discloses:

The coating of any of clauses 1-7, wherein said coating has a tearstrength greater than 30 J/m².

Clause 9 of the description discloses:

The coating of any of clauses 1-7, wherein said coating has a tearstrength greater than 40 J/m².

Clause 10 of the description discloses:

The coating of any of clauses 1-7, wherein said coating has a tearstrength greater than 50 J/m².

Clause 11 of the description discloses:

The coating of any of clauses 1-10, wherein said coating has a tensiletoughness greater than 500 kJ/m³.

Clause 12 of the description discloses:

The coating of any of clauses 1-10, wherein said coating has a tensiletoughness greater than 700 kJ/m³.

Clause 13 of the description discloses:

The coating of any of clauses 1-10, wherein said coating has a tensiletoughness in the range from 500 kJ/m³-1200 kJ/m³.

Clause 14 of the description discloses:

The coating of any of clauses 1-13, wherein said coating is a curedproduct of a curable composition, the curable composition comprising:

-   -   a diisocyanate compound;    -   a hydroxy (meth)acrylate compound; and    -   a polyol compound, said polyol compound having unsaturation less        than 0.1 meq/g;    -   wherein said diisocyanate compound, said hydroxy (meth)acrylate        compound and said polyol compound are present in said        composition in the molar ratio n:m:p, respectively, where n is        in the range from 3.0 to 5.0, m is in the range from 1.50n-3 to        2.50n-5, and p is 2.

Clause 15 of the description discloses:

The coating of clause 14, wherein said diisocyanate compound comprises acompound having the formula:O═C═N—R₁—N═C═Owherein the group R₁ comprises an alkylene group.

Clause 16 of the description discloses:

The coating of clause 15, wherein said group R₁ comprises a4,4′-methylenebis(cyclohexyl) group.

Clause 17 of the description discloses:

The coating of any of clauses 14-16, wherein said polyol compoundcomprises a compound having the formula:H—O

R₂—O

_(x)Hwherein the group R₂ comprises an alkylene group and x is between 40 and100.

Clause 18 of the description discloses:

The coating of any of clauses 14-17, wherein n is in the range from 3.4to 4.6 and m is in the range from 1.60n-3 to 2.40n-5.

Clause 19 of the description discloses:

The coating of any of clauses 14-18, wherein said polyol ispolypropylene glycol having a number average molecular weight in therange from 3000 g/mol to 9000 g/mol.

Clause 20 of the description discloses:

The coating of any of clauses 14-19, wherein said cured productcomprises:

an oligomer, said oligomer comprising:

-   -   a polyether urethane acrylate compound having the molecular        formula:

-   -   and a di-adduct compound having the molecular formula:

-   -   wherein        -   R₁, R₂ and R₃ are independently selected from linear            alkylene groups, branched alkylene groups, or cyclic            alkylene groups;        -   y is 1, 2, 3, or 4;        -   x is between 40 and 100;        -   said di-adduct compound is present in an amount of at least            1.0 wt %.

Clause 21 of the description discloses:

The coating of clause 20, wherein said di-adduct compound is present inan amount of at least 2.35 wt %.

Clause 22 of the description discloses:

The coating of any of clauses 14-21, wherein said coating compositionfurther comprises a mercapto-functional silane compound and aphotoinitiator.

Clause 23 of the description discloses:

An optical fiber comprising:

-   -   a glass core;    -   a glass cladding surrounding and in direct contact with said        glass core; and    -   the coating of any of clauses 1-22, the coating surrounding and        in direct contact with said glass cladding.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention. Since modifications combinations,sub-combinations and variations of the disclosed embodimentsincorporating the spirit and substance of the invention may occur topersons skilled in the art, the invention should be construed to includeeverything within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A coating for optical fibers comprising: a polyol compound, said polyol compound having unsaturation less than 0.1 meq/g; a mercapto-functional silane compound; a Young's modulus less than 1.0 MPa; and a pullout force less than 1.7 lbf/cm when configured with thickness 32.5 μm to surround and directly contact a glass fiber having a diameter of 125 μm in an as-drawn state, said pullout force increasing by less than a factor of 2.0 upon aging said coating on said glass fiber for at least 60 days.
 2. The coating of claim 1, wherein said Young's modulus is less than 0.8 MPa.
 3. The coating of claim 1, wherein said Young's modulus is less than 0.6 MPa.
 4. The coating of claim 1, wherein said pullout force is less than 1.5 lbf/cm.
 5. The coating of claim 1, wherein said pullout force is less than 1.3 lbf/cm.
 6. The coating of claim 1, wherein said pullout force increases by less than a factor of 1.9 upon aging said coating on said glass fiber for at least 60 days.
 7. The coating of claim 1, wherein said pullout force increases by less than a factor of 1.8 upon aging said coating on said glass fiber for at least 60 days.
 8. The coating of claim 1, wherein said coating has a tear strength greater than 30 J/m².
 9. The coating of claim 1, wherein said coating has a tear strength greater than 40 J/m².
 10. The coating of claim 1, wherein said coating has a tear strength greater than 50 J/m².
 11. The coating of claim 1, wherein said coating has a tensile toughness greater than 500 kJ/m³.
 12. The coating of claim 1, wherein said coating has a tensile toughness greater than 700 kJ/m³.
 13. The coating of claim 1, wherein said coating has a tensile toughness in the range from 500 kJ/m³ 1200 kJ/m³.
 14. The coating of claim 1, wherein said coating is a cured product of a curable composition, the curable composition comprising: a diisocyanate compound; and a hydroxy (meth)acrylate compound; wherein said diisocyanate compound, said hydroxy (meth)acrylate compound and said polyol compound are present in said composition in the molar ratio n:m:p, respectively, where n is in the range from 3.0 to 5.0, m is in the range from 1.50n-3 to 2.50n-5, and p is
 2. 15. The coating of claim 14, wherein said diisocyanate compound comprises a compound having the formula: O═C═N—R₁—N═C═O wherein the group R₁ comprises an alkylene group.
 16. The coating of claim 15, wherein said group R₁ comprises a 4,4′-methylenebis(cyclohexyl) group.
 17. The coating of claim 14, wherein said polyol compound comprises a compound having the formula: H—O

R₂—O

_(x)H wherein the group R₂ comprises an alkylene group and x is between 40 and
 100. 18. The coating of claim 14, wherein n is in the range from 3.4 to 4.6 and m is in the range from 1.60n-3 to 2.40n-5.
 19. The coating of claim 14, wherein said polyol is polypropylene glycol having a number average molecular weight in the range from 3000 g/mol to 9000 g/mol.
 20. The coating of claim 14, wherein said cured product comprises: an oligomer, said oligomer comprising: a polyether urethane acrylate compound having the molecular formula:

and a di-adduct compound having the molecular formula:

wherein R₁, R₂ and R₃ are independently selected from linear alkylene groups, branched alkylene groups, or cyclic alkylene groups; y is 1, 2, 3, or 4; x is between 40 and 100; said di-adduct compound is present in an amount of at least 1.0 wt %.
 21. The coating of claim 20, wherein said di-adduct compound is present in an amount of at least 2.35 wt %.
 22. The coating of claim 14, wherein said coating composition further comprises a photoinitiator.
 23. An optical fiber comprising: a glass core; a glass cladding surrounding and in direct contact with said glass core; and the coating of claim 1, the coating surrounding and in direct contact with said glass cladding. 